Cytochrome P450 (P450) enzymes play crucial roles in the clearance of drugs from the circulation, and therefore changes in their activities can significantly influence the therapeutic and adverse effects of a drug on an individual. Infectious and inflammatory diseases cause the down-regulation of many P450s and other drug metabolizing enzymes in the liver, causing impairment of drug clearances. In mice infected with C. rodentium, a model of E. Coli food poisoning in humans, a number of P450 enzymes in the liver are moderately down-regulated. However, CYP4A enzymes are more profoundly affected, as is another drug metabolizing enzyme, i.e. flavin monooxygenase 3 (FMO3). Preliminary evidence suggests that one or more bacterially secreted factors regulate hepatic CYP4A expression in an endotoxin-independent manner. CYP4As have important roles in fatty acid metabolism, control of blood pressure and in oxidative stress. Therefore, it is important to understand how human CYP4A11 is regulated during infection, and to understand whether on not CYP4A regulation is a defensive or adaptive response of the host, or if the invading bacterium could be regulating CYP4As to its own advantage. To address these questions, the regulation of CYP4A11 will be studied in the livers and kidneys of CYP4A11 transgenic mice during C. rodentium infection. This will be complemented by studies in cultured human hepatocytes and in CYP4A11 transgenic mouse hepatocytes, on CYP4A11 regulation by inflammatory cytokines and bacterial products. Transcriptional and proteomic profiling will be used to assess the effects of infection on global gene expression in the liver and to elucidate signaling networks involved in CYP4A and FMO3 down-regulation by factors secreted by bacteria. To identify these factor(s) we will screen known mutants and, if necessary, an enteropathogenic E. coli transposon insertion library to identify mutants that fail to down-regulate these enzymes. This approach will be complemented by biochemical characterization and partial purification of the factor(s). To elucidate the role of CYP4A enzymes in the host response to C. rodentium infection, or as targets of the bacterium's strategy for propagation and survival, the effects will be studied of Cyp4A10-/- and Cyp4A14-/- gene deletion on the pathologies associated with C. rodentium infection.